What is a Pentaquark ? |
| Photon
+ Carbon |
Pentaquark
States |
Until recently only two- and three-quark combinations have been observed in nature, the mesons and baryons, respectively. New experiments have revealed states that are attributed to five-quark combinations. An example is the reaction of photons on carbon nuclei shown in the picture. But it is a puzzle why the states have a much longer lifetime than expected.
Recently Naftali Auerbach, Vladimir Zelevinsky and Alexander Volya have used ideas developed for the nucleus to provide a possible explantion. The idea can be traced back to the phenomenon of "super-radiance" in quantum optics. There are many coherent five-quark states such as the two shown in the picture - a rather tightly bound state on the top and an orbiting state on the bottom. The mixing of these states provides a "trapping" mechanism that gives the long lifetime.
This model is described in their article in Phys. Lett. B 590 (2004) page 45.